Oh my goodness, I am having the exact same problem with my 19 month old! I thought it was because he had been sick or something. We just ignore him - don't go in at all - he hasn't been crying or anything but he can still manage to be up for 3 to 4 hours. It is really dark in his room with no night lights or anything so I have no idea what he does in there for that time.

We sleep on and off between him banging the walls and singing but he is not coping at all during the daytime which is my biggest concern or he has been sleeping in until 11 because he is so tired. I have been calling him my little teenager.

Sorry I don't have any advice, I was just so excited to know I wasn't the only one with a toddler this age doing this ... small things ...